Cosmetic Electrochemistry II: Rapid and Facile Production of Metallic Electrocatalytic Ensembles

We demonstrate a facile methodology for the production of metallic electrocatalytic microdomain ensembles for a range of analytical sensing challenges. A commercially available off‐the‐shelf cosmetic product can change the voltammetric characteristics of a metallic macro‐electrode created electrolytically into that of a random ensemble of metallic microelectrode domains. Proof‐of‐concept is shown for three examples: a palladium ensemble for hydrazine sensing, a gold ensemble for arsenic(III) detection via anodic stripping voltammetry and platinum ensembles for the direct oxidation of arsenic(III). Last we demonstrate that the fabrication of metallic microdomains can be simplified by sputter coating screen printed electrochemical sensing platforms which are beneficially constructed using this cosmetic methodology. Given the facile fabrication and low cost of the underlying electrode substrate and the cosmetic modifier, the widespread implementation of this novel fabrication methodology is expected.     

Development of a simple extraction and clean-up procedure for determination of organochlorine pesticides in soil using gas chromatography–tandem mass spectrometry

A procedure based on QuEChERS extraction and a simultaneous liquid–liquid partition clean-up was developed. The procedure involved extraction of hydrated soil samples using acetonitrile and clean-up by liquid–liquid partition into n-hexane. The hexane extracts produced were clean and suitable for determination using gas chromatography–tandem mass spectrometry (GC–MS/MS). The method was validated by analysis of soil samples, spiked at five levels between 1 and 200 μg kg⁻¹. The recovery values were generally between 70 and 100% and the relative standard deviation values (%RSDs) were at or below 20%. The procedure was validated for determination of 19 organochlorine (OC) pesticides. These were hexachlorobenzene (HCB), α-HCH, β-HCH, γ-HCH, heptachlor, heptachlor epoxide (trans), aldrin, dieldrin, chlordane (trans), chlordane (cis), oxychlordane, α-endosulfan, β-endosulfan, endosulfan sulfate, endrin, p,p′-DDT, o,p′-DDT, p,p′-DDD and p,p′-DDE. The method achieved low limits of detection (LOD; typically 0.3 μg kg⁻¹) and low limits of quantification (LOQ; typically 1.0 μg kg⁻¹). The method performance was also assessed using five fortified soil samples with different physico-chemical properties and the method performance was consistent for the different types of soil samples. The proposed method was compared with an established procedure based on Soxtec extraction. This comparison was carried out using six soil samples collected from regions of Pakistan with a history of intensive pesticide use. The results of this comparison showed that the two procedures produced results with good agreement. The proposed method produced cleaner extracts and therefore led to lower limits of quantification. The proposed method was less time consuming and safer to use. The six samples tested during this comparison showed that soils from cotton growing regions contained a number of persistent OC residues at relatively low levels (<10 μg kg⁻¹). These residues were α-HCH, γ-HCH, heptachlor, chlordane (trans), p,p′-DDT, o,p′-DDT, p,p′-DDD, p,p′-DDE, β-endosulfan and endosulfan sulfate.     

Nanofabrication of gallium nitride photonic crystal light-emitting diodes

We describe a comparison of nanofabrication technologies for the fabrication of 2D photonic crystal structures on GaN/InGaN blue LEDs. Such devices exhibit enhanced brightness and the possibility of controlling the angular emission profile of emitted light. This paper describes three nano lithography techniques for patterning photonic crystal structures on the emitting faces of LEDs: direct-write electron beam lithography, hard stamp nanoimprint lithography and soft-stamp nanoimprint lithography with disposable embossing masters. In each case we describe variations on the technique as well as its advantages and disadvantages. Complete process details have been given for all three techniques. In addition, we show how high performance GaN dry etch techniques, coupled with optical process monitoring can transfer resist patterns into underlying GaN material with high fidelity.     

Approximation of analytical functions by k-positive linear operators in the closed domain

This work treats the problem of convergence for the sequences of linear \(k\) -positive operators on a space of functions that are analytic in a closed domain. By convergence in this space, we mean a uniform convergence in a closed domain that contains the original domain strictly inside itself, while the linear \(k\) -positive operators are naturally associated with Faber polynomials related to the considered domain. Until now, this problem has been solved in the space of functions analytic in an open bounded domain with the topology of compact convergence.     

Decision feedback sequence estimation for unwhitened ISI channelswith applications to multiuser detection

Decision feedback sequence estimation (DFSE), which is a reduced-complexity alternative to maximum likelihood sequence estimation (MLSE), can be used effectively for equalization of intersymbol interference (ISI) as well as for multiuser detection. The algorithm performs very well for whitened (minimum-phase) channels. For nonminimum-phase channels, however, the algorithm is not very effective. Moreover, DFSE requires a noise-whitening filter, which may not be feasible to compute for time-varying channels such as a multiuser direct-sequence code division multiple access (DS-CDMA) channel. Noise-whitening is also cumbersome for applications that involve bidirectional equalization such as the global system for mobile communication (GSM) system. In such conditions, it is desirable to use the Ungerboeck (1974) formulation for sequence estimation, which operates directly on the discrete-time unwhitened statistic obtained from conventional matched filtering. Unfortunately, DFSE based on matched filter statistics is severely limited by untreated interference components. We identify the anticausal interference components, using an error probability analysis. This leads us to a modified unwhitened decision feedback sequence estimator (MUDFSE) in which the components are canceled, using tentative decisions. We obtain approximate error probability bounds for the proposed algorithm. Performance results indicate that the modified algorithm, used on unwhitened channels with relatively small channel correlations, provides similar performance/complexity tradeoffs as the DFSE used on the corresponding whitened minimum-phase channels. The algorithm is especially attractive for multiuser detection for asynchronous DS-CDMA channels with long spreading codes, where it can achieve near-MLSE performance with exponentially lower complexity     

Strong enhancement and extinction of single harmonic intensity in the mid- and end-plateau regions of the high harmonics generated in weakly excited laser plasmas

Strong intensity enhancement or extinction of some single harmonics is observed in high-harmonic generation from 48 fs Ti:sapphire laser pulses propagating through preformed low-excited laser-produced plasmas of various materials (GaAs, Cr, InSb, stainless steel). The intensities of some of the harmonics in the mid- and end-plateau regions vary from ~23-fold enhancement to near disappearance compared with those of the neighboring ones. It is also shown that the observed intensity enhancement (or extinction) can be varied by controlling the chirp of the driving laser radiation.     

π‐Expanded α,β‐Unsaturated Ketones: Synthesis,Optical Properties,and Two‐Photon‐Induced Polymerization

A library of π‐expanded α,β‐unsaturated ketones was designed and synthesized. They were prepared by a combination of Wittig reaction, Sonogashira reaction, and aldol condensation. It was further demonstrated that the double aldol condensation can be performed effectively for highly polarized styrene‐ and diphenylacetylene‐derived aldehydes. The strategic placement of two dialkylamino groups at the periphery of D ‐π‐A‐π‐D molecules resulted in dyes with excellent solubility. These ketones absorb light in the region 400–550 nm. Many of them display strong solvatochromism so that the emission ranges from 530–580 nm in toluene to the near‐IR region in benzonitrile. Ketones based on cyclobutanone as central moieties display very high fluorescence quantum yields in nonpolar solvents, which decrease drastically in polar media. Photophysical studies of these new functional dyes revealed that they possess an enhanced two‐photon absorption cross section when compared with simpler ketone derivatives. Due to strong polarization of the resulting dyes, values of two‐photon absorption cross sections on the level of 200–300 GM at 800 nm were achieved, and thanks to that as well as the presence of the keto group, these new two‐photon initiators display excellent performance so that the operating region is 5–75 mW in some cases.     

Facile and Mild Synthesis and Characterization of Some New Diazo Dyes on the Basis of Schiff Bases in the Presence of Nanocrystalline Magnesium Oxide as a Base Catalyst under Solvent‐free Conditions

In this research, some new diazo dyes including Schiff base have been synthesized by the condensation reaction between ethylenediamine and derivatives of salicylaldehyde containing diazo functional groups in the presence of nanocrystalline magnesium oxide as a solid base catalyst under solvent‐free conditions. Nanocrystalline magnesium oxide has been characterized by XRD, BJH and TEM techniques. The corresponding products have been obtained in excellent yields and high purity. All of the obtained diazo‐Schiff bases are highly colored and can be applicable as useful diazo dyes and characterized by spectroscopy data.     

Chemoselective Route for Synthesis of N‐Aryl‐3‐oxochromeno[2,3‐c]pyrazole‐2(3H)‐carbothioamide Derivatives

A chemoselective route for the synthesis of chromeno[2,3‐c]pyrazole‐2(3H)‐carbothioamide derivatives by a five‐component reaction of salicylaldehyde, malononitrile, NH₂NH₂?H₂O, aryl isothiocyanate, and H₂O in EtOH/AcOH mixture is reported. This new protocol has the advantages of high yields, short reaction times, ease of operation, and simple purification. All structures were confirmed by IR, ¹H‐ and ¹³C‐NMR, and MS analyses. A plausible mechanism for this type of reaction is proposed (Scheme 2).